Linear synchronous motors comprise a longitudinal stator on which at least one translator is freely moveable. A magnetic travelling-field is generated for moving the translator(s). The stator includes separate coil units, each comprising at least one coil. Usually, the magnetic travelling-field is generated by applying a three-phase current to said coil units. One example of a well known linear motor is disclosed in DE 39 00 511 A1. A current with variable frequency and amplitude is applied to the coil units of the longitudinal stator depending on the actual location of the translator, in order to move the translator relative to the stator.
NL 1024992 discloses a prior art linear motion system, which comprises an apparatus for moving carriers in a circulating transport circuit using magnetic movement devices, which comprise magnetic units working together and controllable coil units. Such an apparatus is often used in automated and specific product facilities, where a product is placed on the product carrier. During the circulation through the transport circuit, the product has to undergo several similar process steps. An application of such an apparatus relates to a semiconductor substrate placed on a product carrier, where various ultra-thin layers are to be deposited (e.g. chemical or physical vapour deposition CVD/PVD).
In such an application field, precise control of the movement of the various product carriers through the circulating transport circuit is essential for the correct performance of the various process actions on the products placed on the product carriers. Magnetic movement devices are used to move the product carriers through the transport circuit, particularly where very high requirements are set for the accuracy of the various process actions, such as the placement of an electronic component or the deposition of a semiconductor layer on a substrate.
The actuation occurs without contact between stator and translator, and without detrimental influences that can disturb the movement of the product carriers through the transport circuit, with the possibility to manipulate different product carriers independently of each other. The apparatus corresponding to the prior art comprises sensor devices, which are provided to detect the magnets of one product carrier and on the basis thereof to generate a position signal of the product carrier. This detection signal is used to activate the movement devices for the accurate positioning of the product carrier in the transport circuit. This, in combination with the independently controllable coil units, allows for an activation of each product carrier separately and for movement/position of each product carrier independently of the other product carriers.
In view of this prior art, it is an object of the disclosure to provide a method and an apparatus for controlling such a linear motion system so that a train comprising at least two carriers can be formed.
According to the disclosure a method and an apparatus for controlling a linear motion system, further a corresponding computer program and a computer program product, according to the independent claims are provided. Advantageous embodiments are defined in the dependent claims.